A commonly used method to track the position of a radio signal transmitting device is to use the time difference of arrival (or, equivalently, the phase difference of arrival) at various receivers or receiver antennae (receivers) disposed at known locations, to determine the position of the RF transmitting device. By solving the non-linear equations associated with such systems, the position of the RF transmitting device can be determined. Because phase (θ) and time (t) are related by θ=ωt, where ω is a scalar, phase and time are equivalent systems and subsequent descriptions are denoted by time or time differences, as appropriate.
Typically, position tracking systems require at least three or four receivers at known positions to determine a two-dimensional or three-dimensional position recording of the RF transmitting device. An example of an embodiment can contain a receiver channel that includes one antenna, one receiver, phase correlation circuitry for comparing the RF transmitting device signal's time difference of arrival, ADC circuitry, and a processor for processing the timing data. Many tracking systems use just one processor that receives data from each receiver channel with each receiver channel including both receiver hardware and the antenna.
Certain computer-based applications track the position of an interactive peripheral device (i.e., RF transmitting device) and use that position data to engage a software program requiring high tracking accuracy. In these applications, the RF transmitting device is registered with screen images provided by software. To make this RF transmitting device's operation effective for a user (e.g., to control a cursor on a screen) highly accurate positions are required to provide realistic interaction between the user operating the RF transmitting device and the software program. A signal time of arrival comparison approach for RF transmitting device tracking can provide these higher accuracies.
A problem with such position tracking systems is the reduction in accuracy due to multipath interference and other line-of-sight blockage issues. Multipath interference is a phenomenon whereby a wave from a source travels to a detector via two or more paths and causes the detector to receive two (or more) components of the wave. Complete line-of-sight blockage can occur when an object comes between the source and detector. During a multi-player game, for example, one player can inadvertently block the transmitter used by another player.